1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to an electrical switching apparatus, such as a circuit breaker, having a carrier assembly with a pivot assembly. The invention also relates to carrier assemblies for circuit breakers. The invention further relates to pivot assemblies for circuit breakers.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions.
Many low-voltage circuit breakers, for example, employ a molded housing having two parts, a first half or front part (e.g., a molded cover), and a second half or rear part (e.g., a molded base). The operating mechanism for such circuit breakers is often mounted to the front part of the housing, and typically includes an operating handle and/or button(s) which, at one end, is (are) accessible from the exterior of the molded housing and, at the other end, is (are) coupled to a pivotable pole shaft. Electrical contact assemblies, which are also disposed within the molded housing, generally comprise a conductor assembly including a movable contact assembly having a plurality of movable contacts, and a stationary contact assembly having a plurality of corresponding stationary contacts. The movable contact assembly is electrically connected to a generally rigid conductor of the conductor assembly by flexible conductors, commonly referred to as shunts. The movable contact assembly includes a plurality of movable contact arms or fingers, each carrying one of the movable contacts and being pivotably coupled to a contact arm carrier. The contact arm carrier is pivoted by a protrusion or arm on the pole shaft of the circuit breaker operating mechanism to move the movable contacts into and out of electrical contact with the corresponding stationary contacts of the stationary contact assembly. The contact arm carrier includes a contact spring assembly structured to bias the fingers of the movable contact assembly against the stationary contacts of the stationary contact assembly in order to provide and maintain contact pressure when the circuit breaker is closed, and to accommodate wear.
The accuracy with which circuit breaker components such as, for example, the operating mechanism, the contact arm carrier, the pivotable pole shaft, and the movable and stationary contact assemblies, are mounted with respect to one another within the molded housing of the circuit breaker significantly affects circuit breaker performance. Specifically, accurate mounting configuration of circuit breaker components results in consistent, reliable kinematics of the circuit breaker, and predictable and thus repeatable mechanical, electrical and thermal circuit breaker performance.
In various known low-voltage circuit breakers, a pivot of the contact arm carrier, such as a pivot pin, is pivotably secured directly between the two parts or halves of the molded circuit breaker housing. More specifically, the pin is disposed between a pair of semi-circles which are molded in the first and second halves of the circuit breaker housing, respectively, and are jointed to form the pivot recess for receiving the pivot pin when the two halves of the housing are coupled together. Such a circuit breaker is susceptible to misalignment and, therefore, can be problematic. Moreover, it fails to provide a good dielectric barrier between adjacent poles of the circuit breaker, particularly at the location where the halves of the circuit breaker housing join to form the carrier pivot recesses. At that location, only a relatively weak labyrinth seal (e.g., a seal comprised of small overlaps between the two housing halves), with relatively little wall thickness, exists.
Manufacturing tolerance discrepancies such as, for example, tolerance discrepancies between the first half or front part of the circuit breaker molded housing, and the second half or back part of the molded housing contribute to misalignment between circuit breaker components. Such discrepancies can result in accumulated dimensional error which can cause, for example, binding or excessive looseness in the pivot members of the contact arm carrier.
Space constraints within the molded housing and cost considerations also serve to limit and/or dictate the mounting options which are available for a particular circuit breaker component. For example, in other known low-voltage circuit breakers, the bearing structure for pivotably securing the contact arm carrier to the molded housing comprises a separate component which is coupled to one or both halves of the molded housing by a plurality of fasteners. Such circuit breakers undesirably add to the complexity and expense thereof.
There is, therefore, room for improvement in electrical switching apparatus, such as low-voltage circuit breakers, and in carrier assemblies and carrier pivots therefor.